This invention relates to a primary thermostat for a fryer which is combined with a cooking computer for a fryer by sharing the output of the cooking computer temperature probe, wherein the operation of the cooking computer temperature probe is monitored and upon failure thereof thermostatic control of the fryer is transferred to a backup thermostat extant in the fryer.
Cooking of foods, such as potatoes, fish, chicken, etc., by frying them in hot cooking oil has been popular in restaurants for a long period of time. Restaurants carrying these items on their menus cook them in fryers, the fryers generally comprising a frypot to hold the cooking oil, heating means to heat the oil, and a thermostat to control the operation of the heating means. The heating means for the fryer is usually one of two types, namely either a gas burner mounted under the frypot or one or more electric resistance heating elements immersed in the cooking oil. The thermostat provides for setting a desired temperature and includes means to measure the actual temperature of the cooking oil, and functions to operate the heating means when the cooking oil falls below the desired temperature. Typically, a relay is provided which either turns on a supply valve to the gas burner or current to the electric resistance heating elements under the control of the thermostat.
Originally, the food items were placed in the hot cooking oil, and the thermostat functioned to maintain the cooking oil as close as possible to the desired cooking temperature while cooking proceeded. The time period for which the food items were cooked was determined by the operator on the basis of his observation and judgment. Cooking computers have been developed and are now widely used in conjunction with fryers to achieve more accurate control of the cooking of food items. In general, cooking computers function to cook food items over a time period calculated to achieve the desired degree of doneness, and this is accomplished by adjusting the cooking time period for variations in the temperature of the cooking oil. Therefore, the cooking computers include a temperature probe for continually measuring the temperature of the cooking oil, and the temperature probes used in conjunction with the cooking computers tend to be of high accuracy and quick response so that the computing of the cooking time period is also accurate. Martino et al U.S. Pat. No. 3,326,692 shows an early example of a cooking computer and Barnes U.S. Pat. No. 3,979,056 shows a more recent example of a cooking computer. Thus, a typical restaurant fryer includes a thermostat having its own temperature probe, the thermostat operating to maintain the cooking oil at a desired set temperature, and also has a cooking computer and an associated cooking computer food temperature probe for calculating the cooking time period of food items.
There are certain problems associated with the present installations. In particular, the thermostats of the fryers often do not maintain close control of the temperature of the cooking oil, and fluctuations from the desired temperature are larger than desired. This is partially because temperature probes associated with the fryer thermostats are often of slow response. For example, if a large load of a cold food item is placed in the cooking oil, the temperature of the cooking oil drops rapidly and the fryer temperature probe and thermostat are slow to recognize the drop and turn on the heating means. Also if the fryer temperature probe or thermostat fails, the fryer ceases to operate and the flow of cooked food items to customers is interrupted. A particularly dangerous problem occurs if the thermostat fails with the heating means in its on condition, wherein the temperature of the cooking oil can rise rapidly with the attendant risk of fire.